Cooked burgers that have been sitting out for longer than 2 hours (or 1 hour above 90° F) should be discarded. The reason is that bacteria grow rapidly when cooked ground beef is kept at temperatures between 40° F and 140° F. To prevent foodborne illness, try to refrigerate the cooked burgers as soon as you can.

You can safely keep cooked hamburgers in the refrigerator for 3 to 4 days; they’ll also keep well in the freezer for at least 2-3 months.